The idea to use polymer blends to reduce the amount of carbon black required to reach the percolation threshold is a well-established concept and is described in the following documents: EP0914367 which discloses a process for preparing an electronically-conductive thermoplastic composition having at least two phases, which includes (I) combining an amorphous or semi-crystalline thermoplastic polymer or miscible blend of polymers with an electronically-conductive carbon under conditions sufficient to disperse the conductive carbon, thereby forming a mixture having at least one phase, with at least 60 percent of the carbon dispersed in a first phase which comprises at least 90 percent by weight of the mixture; and (II) combining the mixture obtained from step (I) with an amorphous or semi-crystalline thermoplastic polymer or miscible blend of polymers, at least a portion of which is immiscible in the first phase, thereby forming a composition having at least two phases. U.S. Pat. No. 6,514,608 discloses a semiconductive jacket material for jacketing a cable comprising a minor phase material which is a semicrystalline polymer; a conductive filler material dispersed in the minor phase material in an amount sufficient to be equal to or greater than an amount required to generate a continuous conductive network in the minor phase material; and a major phase material which is a polymer which when mixed with the minor phase material will not engage in electrostatic interactions that promote miscibility. EP971366 discloses a conductive polymer composite material in the form of a (semi)conductive ternary composite having distinct co-continuous phases and comprises a minor phase material comprising a semicrystalline polymer; a conductive filler material dispersed in the minor phase material in an amount sufficient to generate a continuous conductive network in the minor phase material; and a major phase material being a polymer which when mixed with the minor phase material does not engage in electrostatic interactions that promote miscibility, the major phase material having the minor phase material dispersed therein in an amount sufficient to generate a continuous conductive network in the major phase material.
EP971368 discloses a semiconductive material for use in jacketing cables in the form of a ternary composite having distinct co-continuous phases and comprises a minor phase material comprising a semicrystalline polymer; a conductive filler material dispersed in the minor phase material in an amount sufficient to generate a continuous conductive network in the minor phase material; and a major phase material being a polymer which when mixed with the minor phase material does not engage in electrostatic interactions that promote miscibility, the major phase material having the minor phase material dispersed therein in an amount sufficient to generate a continuous conductive network in the major phase material.
Additionally, in EP1619217 is disclosed an insulation layer for cables comprising a heterophasic polymer composition having superior mechanical and electrical properties and being environmentally friendly. The heterophasic polymer composition comprises a polymer matrix and dispersed therein a propylene copolymer having a weight average particle size of less than 1 μm.
In EP1847565 is disclosed an insulation layer for cables, a composition and a process thereof, showing improved stress whitening resistance by maintaining good mechanical and electrical properties and being environmental friendly.
However none of the above documents addresses the objective of providing a semiconductive polymer composition having desired combination balance between mechanical properties both at high and low temperature.